MAMR head with self-aligned write element and microwave field generator

ABSTRACT

The invention discloses a MAMR head that has the STO stack placed at the trailing side of the write element, with both STO and write element completely self-aligned in the cross track direction. A method for defining both the MP and the STO stack geometries in a single step is also described.

FIELD OF THE INVENTION

The invention relates to the general field of perpendicular magneticrecording with particular emphasis on the use of a locally generatedmicrowave field to effectively lower the coercivity of a storage bitwhile it is being (intentionally) written.

BACKGROUND OF THE INVENTION

Microwave assisted magnetic recording, MAMR, is one of several futuretechnologies that are expected to extend perpendicular magneticrecording beyond 1 terabit per square inch. In this scheme, a fieldgenerator is placed in close proximity to the write element to produce ahigh frequency oscillating field in the media film plane. The frequencyrange of the oscillating field could be from 5 GHz to 50 GHz. Because offerromagnetic resonance (FMR), it becomes possible to switch mediagrains at fields below their normal coercivity i.e. a lower write fieldmay be used, but only in the immediate vicinity of the microwaveassisted write element.

The microwave field generator typically is made of a spin torqueoscillator (STO), which resembles a current-perpendicular-to-plane (CPP)GMR or TMR structure in that the current flows perpendicular to thefilm, although the magnetization directions in the stack are differentfrom those of a CPP GMR/TMR sensor. US patent applicationUS2008/0019040A1 (Zhu et al.) provides details of the STO stackstructure.

As shown schematically in FIG. 1, the simplest configuration for STO 11is a tri-layer stack consisting of spin injection layer SIL 12,interlayer IL 13 (non-magnetic metal or insulating barrier), and fieldgenerating layer FGL 14. The SIL magnetization is kept perpendicular tothe film, either by an external magnetic field or through its intrinsicmagnetic anisotropy. When electrons transit the SIL their spins becomepolarized by the magnetization present in the SIL. The resulting spinpolarization is carried into the FGL by electrons that have crossedinterlayer 13. Spin torque oscillation then occurs in the FGL, producingthe oscillating field.

In order to utilize STO for MAMR recording, the STO needs to be placedas close as possible to where the writing occurs i.e. on the trailingside of the write pole. It is also very important for the oscillatingfield from the STO to be perfectly aligned with the write field from themain pole (MP) in the cross track direction so as to retain maximumtrack density.

A routine search of the prior art was performed with the followingreferences of interest being found:

U.S. Patent Application 2009/0059423 (Yamada et al) shows a spin torqueoscillator between a main pole and trailing shield, but no details aregiven as to how it is fabricated.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to provide a MAMR head that is not subject to accidentalerasure of adjoining tracks

Another object of at least one embodiment of the present invention hasbeen for the STO and the MP to always be in perfect alignment.

Still another object of at least one embodiment of the present inventionhas been to provide optional side shields and a leading shield for saidMAMR head.

A further object of at least one embodiment of the present invention hasbeen to provide a method for self-aligning said MAMR head and said MPduring their formation.

These objects have been achieved through the provision of a method thatallows the STO and the MP to be self-aligned. First, layers of materialsfrom which the STO and the MP can be formed are laid over one another,covering the entire work surface. Then a single mask is provided thatdefines the top surface of each STO/MP unit. Ion beam etching is thenused (in combination with this mask) to remove extraneous material allthe way down to the substrate, thereby forming the units.

During etching the angle of the ion beam can be varied according to thedesigner's choice. For example, the ion beam may be maintained at asingle angle throughout which results in a unit having inwardly slopingsidewalls that all lie in a single plane. Alternatively, the ion beamcould be set to initially etch in a vertical direction and then directedaway from the vertical after some preset amount of material has beenremoved.

Six different embodiments of the invention are disclosed including twoways of making contact between the STO and the trailing shield, using anon-magnetic trailing ‘shield’ as a way to reduce sideways flux leakagefrom the MP, and the provision of side and leading shields.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Schematic of the STO stack, showing the SIL, the IL, and theFGL. Additional protective layers, such as Ru, on either side of thestack are not shown.

FIGS. 2 a-2 e. Process flow for our present method of forming a MAMRhead.

FIG. 3 a-3 d. These illustrate embodiments 1, 2, 3, and 4, respectively.

FIGS. 4 a-4 g. Process flow for manufacturing the embodiment 1 structure(ABS view).

FIGS. 4 a′-4 g′. Process flow for manufacturing the embodiment 1structure (cross-section)

FIGS. 5 a-5 d. Process flow for manufacturing the embodiment 2 structure(ABS view).

FIGS. 5 a′-5 d′. Process flow for manufacturing the embodiment 2structure (cross-section).

FIGS. 6 a-6 d illustrate how the above embodiments can be modified toinclude side shields and/or a leading shield.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2 a to 2 e show how we currently form the write element and STOcombination. Note that, although this process and the resultingstructure have been previously employed by the inventor, they are notconsidered to be prior art that is known outside Headway Technology:

FIG. 2 a shows an air bearing surface (ABS) view of main pole 21 onsubstrate 23 embedded in filler insulation 22 (typically though notnecessarily Al₂O₃). STO stack 11 is then deposited over the full uppersurface of both 21 and 22, as shown in FIG. 2 b. This is followed by theformation of etch mask 24 directly over, and as closely aligned aspossible with, main pole 21. See FIG. 2 c. Mask 24 may be either ofphotoresist or it could be a hard mask of a material such as Al₂O₃ orSiN.

All unprotected parts of STO stack 11 as well as about 100-200 Angstromsof main pole 21 and filler insulation 22 are then removed by either ionbeam or reactive ion etching, giving the structure the appearance shownin FIG. 2 d. This is followed (as shown in FIG. 2 e) with the removal ofall residual photoresist or hard mask material. The latter may beselectively removed through reactive ion etching (RIE), using theappropriate chemicals. The process concludes with the replacement of anylost filler insulation, and the formation of trailing shield 25(generally through electrodeposition).

There are several difficulties associated with this process. First,after the main write pole has been formed, precisely aligning the writepole and STO in the cross track direction is very difficult since aseparate photolithography process has been used to define the trackwidth of the STO (FIGS. 2 c and 2 d). Secondly, after the chemicalmechanical planarization (CMP) of the MP (which results in the structureof FIG. 2 a), there is usually some non-planarity right in the MP areaclosest to the final ABS location. This is due to CMP polish ratedifferences between the MP and the surrounding materials. This couldaffect the quality of the STO stack and thus degrade the performance ofthe oscillating field that is generated.

We now disclose several embodiments of the present invention, each ofwhich overcomes the problems that we have described immediately above:

Embodiment 1

Referring now to FIG. 3 a, the MAMR head includes main pole 21, trailingshield (TS) 25, and STO stack 11 (which is sandwiched between MP 21 andTS 25). The MP and the TS also serve as electrodes for the STO stack toensure CPP current flow through STO. The MP has a beveled sidewallgiving it either a trapezoidal or a triangular pole shape for reducedside writing at skew. In the ABS view shown, the STO stack sitting atthe MP trailing edge is self-aligned to the shape and position of theMP, so that the sidewalls of both the STO and the MP are coplanar. Forillustration purposes only, the STO stack has been shown in abottom-to-top (SIL/interlayer/FGL) configuration, but aFGL/interlayer/SIL configuration could equally well have been used.Various additional layers such as a bottom gap, a capping layer, or anyof several possible insertion layers inside the stack are not shown inthe figure.

Embodiment 2

As seen in FIG. 3 b, this embodiment is the same as FIG. 3 a except thattrailing shield 25 includes a lower protrusion that is part of theself-aligned structure, whereby the sidewalls of the protrusion, theSTO, and the MP are all coplanar.

Embodiment 3

Referring now to FIG. 3 c, this is the same as FIG. 3 a except that atop portion of MP 21 has a substantially vertical sidewall thatcontinues upward through STO 11 all the way to the underside of TS 25.

Embodiment 4

Referring now to FIG. 3 d, this is the same as FIG. 3 a except that MP21 has a substantially vertical side wall that continues upward throughSTO 11 as well as through a downward protruding portion on the undersideof TS 25, said protrusion extending for a distance (e.g., 20 nm) belowthe MP trailing edge.

Embodiment 5

The geometry for this embodiment can be the same as that of any thepreceding four embodiments, but the trailing ‘shield’ is formed from anon-magnetic metal for the sole purpose of serving as an electrode. As aconsequence, the write pole becomes a mono-pole head, whose write fieldperpendicular to the media is stronger than that of the preceding fourembodiments since it has no significant MP-to-TS field perpendicular tothe STO stack. For this embodiment, magnetization of the STO in adirection perpendicular to the stack has to be maintained by some othermechanism such as crystalline magnetic anisotropy.

Embodiment 6

This embodiment can have the form of any of embodiments 1-5, except thatit also has side shields (separated from the MP by a non-magnetic gap)and, optionally, a leading shield.

Method of Making the Structures:

We will now describe process flows for manufacturing embodiments 1 (FIG.3 a) and 2 (FIG. 3 b). Each step is shown in two views: 4 x (or 5 x)which are ABS views and 4 x′ (or 5 x′) which are cross-sections madethrough the center of main pole 21. The broken vertical line that ispresent in all the cross-sectional views represents the future ABSplane.

The first four steps are common to both processes. These are illustratedin FIGS. 4 a-4 d:

The process begins, as shown in FIGS. 4 a and 4 a′, with the depositiononto substrate 23 of material suitable for the formation of main pole21. This is followed by the deposition of unpatterned STO stack 11 asshown in FIGS. 4 b and 4 b′. Next, as seen in FIGS. 4 c and 4 c′, mask44 (photoresist or hard) is formed on STO stack 11 and then subjected toIBE at an angle away from vertical of between 15 and 75 degrees, with 30degrees (±10 degrees) being preferred, so as to form pedestal 43 which,as shown, has inwardly sloping sidewalls.

The first of the final three steps for forming embodiment 1 isillustrated in FIGS. 4 e and 4 e′. First, mask 44 is stripped away. Thestructure is then embedded in fresh filler insulation 22, followingwhich it is planarized, giving it the appearance shown in FIG. 4 e. Notethat layer 22 is present only outside MP 21 and STO 11 so does notappear in FIG. 4 e′.

In the next step, as shown in FIG. 4 f′, starting between 0.03 and 0.2microns back from the plane of the future ABS, STO layer 11 is removedand replaced with additional filler insulation 22. The process concludeswith the deposition of trailing shield 25 whose lower surface is singleplane that contacts STO 11 with no downward protrusion at its point ofcontact therewith.

FIG. 5 shows the process flow for making the embodiment 2 structure(FIG. 3 b). As already noted, FIGS. 5 a and 5 a′ proceed from FIGS. 4 dand 4 d′ respectively. The principal difference between FIG. 4 e andFIG. 5 a is that the remaining portion of mask 44 is left in place whenadditional filler 22 is deposited and subsequently planarized. Only thenis the residue of mask 44 stripped away, giving the structure theappearance illustrated in FIGS. 5 b and 5 b′.

Then, as shown in FIG. 5 c′, starting between 0.03 and 0.2 microns backfrom the plane of the future ABS, STO layer 11 is removed and replacedwith additional filler insulation 22. Thus, as seen in FIG. 5 c, the topsurface of STO 11 is lower than the top surface of filler insulationlayer 22.

The process concludes, as shown in FIGS. 5 d and 5 d′, with thedeposition of trailing shield 25 whose lower surface protrudes downwardsin the area where it overlies STO 11 in order to make contact therewith.

A detailed description of the processes for forming embodiments 3 and 4will not be presented since these are similar to the steps used to formembodiments 1 and 2 respectively, the main difference being the detailsof how step 3 (shaping pedestal 43 as shown in FIGS. 4 c and 4 d) isexecuted. For example, the profiles generated for FIGS. 3 a and 3 bwould be achieved by maintaining a fixed angle for the ion beamthroughout its etching time, but, to generate structures 3 c and 3 d, avertical beam is used initially and then changed to an angled beam whenetching of the main pole starts.

Embodiment 6 it can be made by replacing step 5 (FIGS. 4 e and 5 a) withthe formation of non-magnetic side gap 63 and then electroforming sideshields 61 instead of using filler insulation as before. The leadingshied can be deposited on non-magnetic substrate 23 at the beginning ofstep 1 (FIG. 4 a).

SUMMARY

The STO is formed in a one step process that ensures a self-alignedstructure that is perfectly aligned with respect to the trailing edge ofthe MP, including, if opted for, a downward protrusion therefrom.

Since they are in perfect alignment, substituting a MAMR head for aconventional one does not lead to any loss of cross-track resolution.

The STO is formed on a flat surface thereby improving stack quality anddevice performance.

1. A method to manufacture a self-aligned microwave assisted magneticrecording (MAMR) head, comprising: providing a substrate and depositingthereon a layer of material suitable for the formation of a main pole;depositing an unpatterned spin torque oscillator (STO) stack on saidlayer of material suitable for the formation of a main pole; forming amask, that defines said MAMR head, on said unpatterned STO stack;subjecting said unpatterned STO stack and mask to ion beam etching (IBE)that is directed to be at an angle relative to vertical, until saidsubstrate is reached, thereby forming a pedestal that has inwardlysloping sidewalls; encapsulating said pedestal in a layer of fillermaterial to form a structure and then planarizing said structure;selectively removing said STO stack from an area that extends away froma future ABS plane of said MAMR for a distance; replacing all of saidselectively removed STO stack with additional filler material; and thendepositing a trailing shield layer that contacts both said layer offiller material and said STO stack.
 2. The method recited in claim 1wherein the step of encapsulating said pedestal in a layer of fillermaterial to form a structure and then planarizing said structure,further comprises: first, stripping said mask away; and then depositingsaid layer of filler material, whereby said STO stack and said layer offiller material have coplanar top surfaces.
 3. The method recited inclaim 1 wherein the step of encapsulating said pedestal in a layer offiller material to form a structure and then planarizing said structure,further comprises: while leaving said mask in place, depositing saidlayer of filler material; then planarizing said structure to give it atop surface; and then stripping away said mask whereby said STO stack'stop surface is between 50 and 500 Angstroms lower level than saidstructure's top surface.
 4. The method recited in claim 1 wherein thestep of subjecting said unpatterned STO stack and mask to ion beametching (IBE), further comprises: etching said unpatterned STO stack andsaid mask with a vertically directed ion beam until said layer ofmaterial suitable for the formation of a main pole is reached; and thendirecting said ion beam to be at an angle relative to vertical andetching until said substrate is reached.
 5. The method recited in claim1 wherein the step of subjecting said unpatterned STO stack and mask toion beam etching (IBE), further comprises: etching said unpatterned STOstack and said mask with a vertically directed ion beam until said ionbeam reaches a level that is between 50 and 500 Angstroms below saidlayer of material suitable for the formation of a main pole; thendirecting said ion beam to be at an angle relative to vertical andetching until said substrate is reached.
 6. The method recited in claim1 wherein said trailing shield layer is formed from electricallyconductive non-magnetic material whereby said trailing shield serves asan electrode and a main pole formed from said layer of material suitablefor the formation of a main pole becomes a mono-pole head that has nosignificant field normal to said STO stack, thereby improvingwritability.
 7. The method recited in claim 1 wherein the step ofreplacing all of said selectively removed STO stack with additionalfiller material further comprises using magnetic material for saidfiller material thereby providing said MAMR head with side shields. 8.The method recited in claim 7 further comprising, prior to depositing alayer of material suitable for the formation of a main pole, depositinga layer of magnetic material to serve as a leading shield.
 9. The methodrecited in claim 1 wherein said angle relative to vertical of the ionbeam is in a range of from 15 to 75 degrees.
 10. The method recited inclaim 1 wherein said STO stack has been optimized for microwavegeneration in a range of from 5 to 50 GHz.
 11. The method recited inclaim 1 wherein said distance over which said area extends away from afuture ABS plane is in a range of from 0.03 to 0.2 microns.
 12. Aself-aligned microwave assisted magnetic recording (MAMR) head having anair bearing surface (ABS), comprising: a substrate on which is a mainpole (MP) having first inwardly sloping sidewalls; on, and in contactwith, said MP, a spin torque oscillator (STO) having second inwardlysloping sidewalls; said STO extending away from said ABS for a distance;said STO and said MP being in perfect alignment with one another wherebywhere said MP and STO contact one another no exposed horizontal surfaceis present; over said MP, a trailing shield (TS) having a lower surface,part of which contacts said STO; and filler material located betweensaid substrate and said TS on both sides of said MP and STO.
 13. Theself-aligned MAMR head described in claim 12 wherein said TS lowersurface is a single plane.
 14. The self-aligned MAMR head described inclaim 12 wherein said TS contacts said STO through a protrusion thatextends downwards from said TS lower surface for a distance of between50 and 500 Angstroms.
 15. The self-aligned MAMR head described in claim12 wherein said STO has vertical sidewalls and said MP has sidewallsthat are vertical for a distance of between 50 and 500 Angstroms belowsaid STO and, from there on down, sidewalls that slope inwards at anangle between 4 and 20 degrees from vertical.
 16. The self-aligned MAMRhead described in claim 12 wherein said trailing shield layer has beenformed from electrically conductive non-magnetic material, whereby saidtrailing shield serves as an electrode and said MP is a mono-pole headthat has no significant field normal to said STO stack, therebyimproving writability.
 17. The self-aligned MAMR head described in claim12 wherein said filler material is magnetic whereby said MAMR head hasside shields.
 18. The self-aligned MAMR head described in claim 17further comprising a layer of magnetic material between said MP and saidsubstrate that serves as a leading shield.
 19. The self-aligned MAMRhead described in claim 12 wherein said STO is optimized for microwavegeneration in a range of from 5 to 50 GHz.
 20. The self-aligned MAMRhead described in claim 12 wherein said distance that said STO extendsaway from said ABS is in a range of from 0.03 to 0.2 microns.